Fixes - gRPC management api errors when version not specified

[harshita-meena]

Description

Running gRPCurl command without a version (even though it is optional) gives

, this fix ensures that not specifying version with gRPC works too just like REST API.
grpcurl -plaintext -d '{"model_name": "toy-ranker", "customized": true}' -proto serve/frontend/server/src/main/resources/proto/management.proto localhost:7071 org.pytorch.serve.grpc.management.ManagementAPIsService/DescribeModel

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